It is known that a significant amount of air drag results when a vehicle travels over a roadway; this is due to an area of low pressure created at the rear end of the vehicle. For example, with a tractor-trailer type vehicle, the air makes a sharp bend around the squared-off back of the trailer, thus causing turbulence and drag. To overcome this problem, engine power is required and therefore fuel. Furthermore, the turbulence also causes poor visibility in rainy conditions and an accumulation of dirt on the back of trailers.
In the trucking industry, the aerodynamics of vehicles is a growing concern. Tests indicate that fuel savings from aerodynamic improvements are equivalent to fuel savings attained by a chassis weight reduction and require fewer services to maintain. The air resistance or aerodynamic drag of the vehicle increases the power needed by the engine as the speed increases. It is known that a tractor-trailer needs about 100 HP to overtake the air drag at a speed of 55 MPH. Approximately half the energy reaching the drive wheels is required to overcome air resistance at cruising speed. Recent tests reveal that the square back end contributes approximately to 30% of the air drag. Therefore, the addition of aerodynamic device, such as a rear defector, diminishes the air drag and results in lower fuel consumption.
Various devices have been proposed to reduce air drag.
One air reducing apparatus may be found described in U.S. pat. No. 4,214,787 issued Jul. 29, 1980 to Chain wherein a pair of trim panels are pivotally connected to the rear end of the vehicle with control means connected between each trim panel and the rear end of the vehicle for maintaining the trim panel in an upward position when the vehicle is moving at a rate exceeding a pre-determined minimum velocity. The drag reducing apparatus described in this patent includes a control assembly, which automatically controls the movement of the trim panels between an operating position and a storage position adjacent the vehicle doors. The control system comprises a panel actuator in the form of a ram, which is responsible to the application of pressurized fluid or air by the operator of the vehicle to maintain the panel in the drag reducing position. However, in this drag apparatus, the ram construction does not enable the doors to be moved between a closed position to a completely opened position where the doors are adjacently parallel to the sides of the trailer vehicle.